Propionate kinase

Triose phosphate isomerase, in converting dihydroxyacetone phosphate into glyceraldehyde 3-phosphate, catalyzes the transfer of a hydrogen atom from C-1 to C-2, that is, catalyzes an intramolecular oxidation-reduction. And in essence, after the enzyme reaction, the carbons C-1, C-2 and C-3 of the starting glucose to become equivalent,  chemically indistinguishable, from the carbons C-6, C-5 and C-4, respectively.
Therefore, the net result of the the last two steps of glycolysis is the production of two molecules of glyceraldehyde 3-phosphate .
The ΔG°’ of the reaction is of kJ/mol ( kcal/mol), while the ΔG is kJ/mol ( kcal/mol). Although at equilibrium dihydroxyacetone phosphate represent about 96% of the trioso phosphates, the reaction proceeds readily towards the formation of glyceraldehyde 3-phosphate because of the subsequent step of the glycolytic pathway that removes the glyceraldehyde 3-phosphate produced.
One of the distinguishing features of triose phosphate isomerase is the great catalytic efficiency. The enzyme is in fact considered kinetically perfect . Why?  The enzyme enhances the isomerization rate by a factor of 10 10 compared with that obtained with a catalyst such as acetate ion. Indeed, the K cat /K M ratio for the isomerization of glyceraldehyde 3-phosphate is equal to 2×10 8 M -1 s -1 , value close to the diffusion-controlled limit. Thus, the rate-limiting step in the reaction catalyzed by triose phosphate isomerase is diffusion-controlled encounter of enzyme and substrate.
From the energetic point of view, the last two steps of glycolysis are unfavorable, with ΔG°’ of kJ/mol  ( kcal/mol), whereas the net ΔG°’ of the first five reactions is of kJ/mol ( kcal/mol), with a K eq of about . And it is the free energy derived from the hydrolysis two ATP that, under standard-state conditions, makes the value of the overall equilibrium constant close to one. If instead we consider ΔG, it is quite negative, - kJ/mol (- kcal/mol).

Adverse effects of testosterone supplementation may include increased cardiovascular events (including strokes and heart attacks ) and deaths based on three peer-reviewed studies involving men taking testosterone replacement. [51] In addition, an increase of 30% in deaths and heart attacks in older men has been reported. [52] Due to an increased incidence of adverse cardiovascular events compared to a placebo group , a Testosterone in Older Men with Mobility Limitations (TOM) trial (a National Institute of Aging randomized trial) was halted early by the Data Safety and Monitoring Committee . [53] On January 31, 2014, reports of strokes , heart attacks , and deaths in men taking FDA-approved testosterone-replacement led the FDA to announce that it would be investigating the issue. [54] Later, in September 2014, the FDA announced, as a result of the "potential for adverse cardiovascular outcomes", a review of the appropriateness and safety of Testosterone Replacement Therapy (TRT). [55] [56] [57] The FDA now requires warnings in the drug labeling of all approved testosterone products regarding deep vein thrombosis and pulmonary embolism . [58]

The Endocrine Society recommends against the therapeutic use of DHEA-S in both healthy women and those with adrenal insufficiency , as its role is not clear from studies performed so far. [30] The routine use of DHEA-S and other androgens is discouraged in the treatment of women with low androgen levels due to hypopituitarism , adrenal insufficiency , menopause due to ovarian surgery, glucocorticoid use, or other conditions associated with low androgen levels; this is because there are limited data supporting improvement in signs and symptoms with therapy and no long-term studies of risk. [30]

Propionate kinase

propionate kinase


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